Activated lymphocytes are used as a modality of immunotherapy, especially for cancer treatment. Our studies of activated killer cells are in two areas: (A) Effect of aging on cytolytic T lymphocytes (CTL) activity, using a murine model in vitro and in vivo, and (B) Activation of natural killer (NK) cells to produce lymphokine activated killer (LAK) activity, using a human model in vitro. Project (A), CTL and aging: (1) Interleukin (IL)-12 augments the generation of alloantigen-specific CTL through a pathway not independent of the stimulation of interferon-gamma. The effect is dependent upon T cells, and independent of NK cells. IL-12 augments the development of CTL by spleen cells from aged mice in vitro to the level of that generated by spleen cells from young mice in the absence of IL-12. (2) The effect of IL-12 vivo was determined in tumor-bearing and normal mice of varying ages. Although IL-12 treatment retarded tumor growth in young and aged mice, it reduced the ability to generated primary and secondary CTL ex vivo. The reason for this was primarily due to the peripheral expansion of immature cells because mature CD4 and CD8 T cells were completely functional. (3) Studies are underway to examine alterations in expression of T cell antigen receptor components with aging, and the potential impact on signaling pathways. Project (B), NK and LAK: (1) Studies on the "reverse killing" by NK-sensitive "target cells" of IL-2-stimulated but not native NK cells has revealed the involvement of leukocyte integrins. (2) Signaling through Fas can also induce apoptosis of IL-2-activated but not native NK cells. (3) Signaling by IFN-alpha, IL-12 and IL-2 in primary human NK cells involves differential use of JAK kinases and STAT proteins, and the differential use of these signaling molecules may explain the different but yet overlapping effects of these cytokines on NK cells. (4) IL-12 and IL-2 can synergize in the augmentation of NK activity, and the augmentation is associated with increased transcription of genes encoding for perforin and granzymes. (5) Studies on the regulation of oxidation-reduction regulation of human NK cell activity suggest the involvement of alterations in the cell cycle.